Fracture resistance of dentin-composite interfaces using different adhesive resin layers

Objectives: The objective of this study was to study the effect of different adhesive layers on the interfacial fracture toughness (KICi) of dentin-resin composite interfaces. Methods: Miniature short-rod fracture toughness specimens containing a chevron-shaped dentin-bonded interface along their midplane were used for testing. Each interface zone contained a thinned (one coat of unfilled adhesive resin, air-thinned), one-layer (one coat of unfilled adhesive resin, brush-thinned), two-layer (two coats of unfilled adhesive resin, brush-thinned), 10% filled or 45% filled adhesive resin layer. After storage in distilled water at 37°C for 24 h, the fracture toughness test specimens were loaded in tension at an extension rate of 0.5 mm/min until fracture and the KICi were determined. The results were analysed by ANOVA and Fisherʹs LSD test (p<0.05). Scanning electron microscopy was used to examine representative fracture surfaces. Results: There were no significant differences in mean KICi among the different unfilled adhesive resin layer groups. SEM examination of these specimens showed that fracture generally occurred between the resin-infiltrated layer and adhesive resin layer during interfacial fracture toughness testing. The mean KICi for the 10% filled groups was not significantly different from the unfilled groups. The 45% filled group, however, demonstrated the highest KICi values, the thickest adhesive resin layer under SEM examination, and a fracture path through the adhesive resin layer. Conclusions: There were no significant differences in KICi when the unfilled adhesive resin was used despite different application methods. The 45% filled adhesive resin improved the properties of the dentin-composite interface with respect to both interfacial fracture resistance and dentinal seal after fracture.